The invention relates to systems and slurries for polishing semiconductor substrates.
To meet the needs for larger scale integration, which demands more metal and dielectric layers in devices, the surface topography of the substrate must exhibit exact depth of focus for sub-micron lithography. As discussed in U.S. Pat. No. 6,663,472, chemical mechanical polishing (CMP) is typically used for polishing materials, such as semiconductor substrates and precision optical components, to a high degree of planarity and uniformity. The process is used to initially planarize semiconductor substrate and is also used to remove uneven topography created during the forming of the sub-micron circuitry on the substrate. Where the substrate is to be further processed, such as by photolithography and etching, to create integrated circuit structures, any thickness variation in the planarized layer makes it difficult to meet the fine resolution tolerances required to provide high yield of functional die on a substrate. CMP is typically used in planarizing interlayer insulating films and in shallow-trench separation, because it can completely (both globally and locally) planarize layers to be exposed, reducing the burden on exposure techniques and stabilizing the production yield.
Another application of CMP is to form metal features inlaid in a dielectric layer (in some cases, it is also called damascene), in which CMP is utilized as a method of patterning. In the above mentioned patterning process, trenches are first etched into the dielectric layer, metal layer is next deposited, and finally excess metal is removed using CMP, leaving metal features co-planar with the dielectric layer surface.
A conventional CMP process involves supporting and holding the substrate against a rotating polishing pad that is wetted with polishing slurry and at the same time applying a pressure against the rotating pad. The pH of the polishing slurry controls the chemical reaction, for example, the oxidation of the chemicals that make up the insulating layer of the substrate. The polishing pad is typically made from non-fibrous polyurethane or a polyester-based material. The pad hardness is typically about between 50 and 70 durometers. Polishing pads used with semiconductors are commercially available in a woven polyurethane material. The polishing slurry, which typically includes an abrasive material, is maintained on the polishing pad to modify the polishing characteristics of the pad in order to enhance the polishing and planarization of the substrate.
The CMP polishing action is typically aided by a slurry which includes for example, small abrasive particles such as silica (SiO2) or alumina (Al2O3) that abrasively act to remove a portion of the material on the surface being polished. Additionally, the slurry may include chemicals that react with the process surface to assist in removing a portion of the surface material, the slurry typically being separately introduced between the wafer surface and the polishing pad. During the polishing or planarization process, the wafer is typically pressed against a rotating polishing pad. In addition, the wafer may also rotate and oscillate back and forth over the surface of the polishing pad to improve polishing effectiveness.
As discussed in U.S. Pat. No. 6,638,328, typical CMP polishing slurries contain an abrasive material, such as silica or alumina, suspended in an oxidizing, aqueous medium. There are various mechanisms disclosed in the prior art by which metal surfaces can be polished with slurries. The metal surface may be polished using a slurry where a surface film is not formed causing the process to proceed by mechanical removal of metal particles. In using this method, the chemical dissolution rate should be slow in order to avoid wet etching. A more preferred mechanism continuously forms a thin, soft, and abradable layer through a reaction between the metal surface and one or more components in the slurry such as a complexing agent and/or a film forming layer such as an oxidizer. The thin abradable layer is then removed in a controlled manner by mechanical action. In competing with mechanical action, a thin passive film is formed on the surface and controls the wet etching process. Controlling the chemical mechanical polishing process can be easier with this approach. There are also several different types of slurries used in the CMP process. Common abrasives include silica (SiO2), alumina (Al2O3), ceria (CeO2), titania (TiO2), and zirconia (ZrO2).
Polymers serving as the photo resist, passivation material, and low k ILD materials, among others, have been widely used for manufacturing various IC devices such as DRAM, SRAM, MEMS, imaging devices and CPU, among others. Increasingly, to enhance performance, a thinner and/or a more planar polymer film is desired. As device feature size continues to shrink, planarity requirements become increasingly stringent and such polymer materials need to be planarized. While chemical mechanical polishing (CMP) is a viable planarization method for IC devices, there have been no CMP slurries developed specifically for polymer CMP. Using un-optimized CMP slurries for polymer polishing can result in many issues. For example, on occasions, the polymer is not cured completely to get a high RR of polishing using conventional oxide slurry. This method causes at least two drawbacks, one is the difficulty in CMP process control, for (1) the softness of the film is sensitive to even minor curing variations; (2) it is hard to get a proper polishing stop for the soft film if only mechanical polishing is used; and (3) mechanical polishing results in higher non-uniformity, scratch and residue. Another drawback is after polishing, the film needs to be cured for a second time, which lowers the throughput and is not cost effective.
On occasions, the polymer surface has been treated with N2O or O2 plasma before the polishing so that a desirable removal rate and stop layer can be obtained. However, this solution is slow and not cost effective. Moreover, the defect issue can also be increased because the process uses oxide slurry rather than slurry designed specifically for the polymer film. In addition, because both the polymer film and the polishing pad are hydrophobic, during the polishing, wafer dropping can increase due to the friction between the polymer film surface and the polishing pad.